Prestressable layer system for partition glass

ABSTRACT

A low-emissivity multilayer system, capable of being bent and prestressed, for glazing panes, with silver as functional layer, comprises a sacrificial metal layer of Ti or an alloy of Ti and Zn and/or Al placed above the silver layer, antireflection dielectric layers and an oxide, nitride or oxynitride covering layer. The sacrificial metal layer contains chemically bonded hydrogen. An optionally Al- and/or In-doped ZnO layer is adjacent to the sacrificial metal layer. The covering layer consists of a titanium compound. Multilayer systems of this type can be manufactured relatively inexpensively and have a high hardness and a high chemical resistance. Their color parameters are very reproducible, even in the case of a heat treatment at high temperature.

The invention relates to a low-emissivity multilayer system, capable ofbeing highly stressed thermally, for glazing panes, with silver asfunctional layer, a sacrificial metal layer placed above the silverlayer, antireflection dielectric layers and an oxide, nitride oroxynitride covering layer.

Low-emissivity multilayer systems must be able to be highly stressedthermally when the coated glazing panes undergo a bending and/orprestressing operation. Although thermally stable layers are notnecessary when the panes are coated only after the bending andprestressing, this has the disadvantage that it is not always possibleto avoid coating defects. These defects result from the fact that theheat treatment operation often causes local modifications of the glasssurface which become visible after the coating operation. In particular,coating before the heat treatment operation also has the economicadvantage of simplifying the coating operation because it is possible tocoat large panes in large industrial plants. The desired shapes are thencut from the large coated panes and bent and/or prestressed in theaccustomed manner.

Multilayer systems capable of being highly stressed thermally are knownin various embodiments. In a first group of multilayer systems that canbe highly stressed thermally, the antireflection layers each consist ofSi₃N₄ and are separated from the silver functional layer by thin metalsacrificial layers of CrNi. Multilayer systems that have this structureare, for example, disclosed in documents EP 0 567 735 B1, EP 0 717 014B1, EP 0 771 766 B1, EP 0 646 551 B1 and EP 0 796 825 A2. The multilayersystem disclosed in EP 0 883 585 B1 also belongs to this group, but inthis case the sacrificial metal layer consists of Si. Although suchmultilayer systems are thermally very stable, they are very expensive tomanufacture because of the known problems that arise when sputteringnitrides. Furthermore, sputtering relatively thick Si₃N₄ layers remainsproblematic because of mechanical stresses in the layers.

Belonging to the second group of multilayer systems capable of beinghighly stressed thermally are those which, in addition to nitride layerssuch as Si₃N₄ or AlN, also have oxide layers, in particular in theregion of the covering layer. For example, DE 196 40 800 C2 discloses amultilayer system in which a nitride or oxynitride interlayer of themetal of the sacrificial metal layer is placed between the metalblocking layer and the oxide or nitride covering layer. Anothermultilayer system of this type, known from DE 101 05 199 C1, ischaracterized in that an Si₃N₄ or AlN layer is placed between the silverlayer and the sacrificial metal layer. In the multilayer system knownfrom EP 0 834 483 B1, a TiO₂ interlayer with a thickness of at least 5nm is placed between a Ti sacrificial metal layer and the coveringlayer, and a covering layer made of a Bi, Sn or Zn oxide, nitride oroxynitride, or an oxide, nitride or oxynitride of a mixture of thesemetals, is placed on this interlayer. Both Si₃N₄ or AlN interlayers andthick TiO₂ layers are complicated to manufacture. Furthermore, thickTiO₂ layers with a high refractive index impose high thicknessuniformity requirements, and even small variations in the thickness ofthe layer may result in tinting errors after the prestressing operation.

In a third group of multilayer systems capable of being highly stressedthermally, the individual layers consist purely of oxide layers, withthe exception of the functional layer and of the sacrificial metallayer. Since oxide layers can for the most part be sputtered without anyproblem, such multilayer systems are inexpensive to manufacture.However, in this case, the sacrificial metal layer has a relativelylarge thickness. A multilayer system of this type is disclosed, forexample, in DE 198 52 358 C1. The sacrificial metal consists in thiscase of an alloy of aluminum with one or more of the elements Mg, Mn,Cu, Zn and Si as alloying components.

Also disclosed, in EP 0 233 003 B1, is a pure oxide multilayer systemfor glazing panes, which system has to be suitable for undergoing abending and/or prestressing operation. In this known multilayer system,an Al, Ti, Zn or Ta layer with a thickness of 4 to 15 nm is placed abovethe silver layer. Preferably, an Al, Ti, Zn or Ta layer is also placedbeneath the silver layer.

DE 39 41 027 C2 discloses an oxide multilayer system which must besuitable for undergoing bending and/or prestressing. In this knownmultilayer system, a ZnO layer with a thickness of at most 15 nm isplaced beneath the silver layer, and the silver layer is covered with anoxide of a sacrificial metal of the group: titanium, aluminum, stainlesssteel, bismuth, zinc, or a mixture of these oxides, which is formed bydeposition of the sacrificial metal and its conversion into an oxide.

The reflection color of all the known multilayer systems is visiblymodified to a greater or lesser extent after the heat treatment neededto bend and/or prestress the panes. As a general rule, they also have anincreased emissivity after the heat treatment and an increased lightscattering factor. Because of the change in reflection color, coatedpanes that have been thermally treated and incorporated into the samewall cladding alongside panes that have not been thermally treated, butdo have the same multilayer system, can be recognized with the nakedeye. For this reason, another prestressable multilayer system whoseproperties are comparable to those of a thermally untreated multilayersystem is consequently required.

Simultaneous compliance with the three important conditions, namelyconstancy of closely defined reflection color and, if possible, noincrease, or only a slight increase, in the light scattering factor andin the emissivity as a result of the heat treatment operation, is allthe more difficult to achieve the higher the requirements in terms ofcolor neutrality of the multilayer system.

The problem on which the invention is based therefore consists in how todevelop a multilayer system of neutral color with essentially oxideantireflection layers which, after a heat treatment operation, forexample necessary for bending and/or prestressing the glazing pane,exhibit in reflection essentially the same color parameters as apredetermined oxide multilayer system that has not been heat treated,and in which the heat treatment also increases the light scatteringfactor and the emissivity as little as possible. At the same time, themultilayer system must have a high hardness and a high chemicalresistance.

According to the invention, this problem is solved in that thesacrificial metal layer consists of Ti or an alloy of Ti and Zn and/orAl, and contains chemically bonded hydrogen, and in that a ZnO layeroptionally doped with Al and/or In is joined to the sacrificial metallayer and in that the covering layer consists of a titanium compound.

Multilayer systems having the structure according to the invention maybe manufactured relatively inexpensively and have a high hardness and ahigh chemical resistance. However, in particular they are characterizedin that, with a heat treatment operation, even at high temperature,their color appearance may be modified in a controlled and veryreproducible manner and that they exhibit only a very small increase inthe light scattering factor and a low emissivity.

Obviously, the composition of the sacrificial metal layer that issputtered in an Ar/H₂ working gas atmosphere plays a particular role.Since metallic Ti has the property of bonding to hydrogen, theprotective effect of the sacrificial metal layer with respect to thesilver layer is further enhanced by a reducing “hydrogen buffer”. Thehydrogen in the sacrificial metal layer may be detected using suitableanalytical methods.

Titanium alloys containing 50 to 80 wt % Ti and 20 to 50 wt % Al forexample have proved to be particularly suitable for the sacrificialmetal layer.

The desired result is considerably helped by placing the optionally Al—or In-doped ZnO layer directly on the sacrificial metal layer. This ZnOlayer may have a thickness such that the layer itself alreadyconstitutes the antireflection layer, in such a way that the coveringlayer immediately follows this ZnO layer. However, it is also possibleto provide only a relatively thin ZnO layer, which then acts as apartial layer of the antireflection layer, whereas the partial layer ofthe antireflection layer that is joined to it consists, for example, ofSnO₂. However, in this case it is necessary for the thickness of the ZnOlayer to be at least 3 nm.

The covering layer of the multilayer system is preferably a mixed oxideof spinel structure, but binary alloys of the Ti/Al type are alsosuitable. The following compounds are particularly well suited for thecovering layer: Al:ZnO/TiO₂, Al:ZnO/Ti, Zn_(x)Sn_(y)O_(z)/TiO₂,Zn_(x)Sn_(y)O_(z)/Ti, Zn_(x)Ti_(y)Al_(z)O_(r), Ti_(x)Al_(y)O_(z),Ti_(x)Al_(y), Ti_(x)Al_(y)N_(z), Ti_(x)Al_(y)O_(z)N_(r),Zn_(x)Sn_(y)Sb_(z)O_(r)/TiO₂, Zn_(x)Sn_(y)Sb_(z)O_(r)/Ti orZn_(x)Sn_(y)Al_(z)O_(r)/TiO₂. Where there are titanium alloys, theyrepresent the state of the covering layer before the heat treatmentoperation, during which they are then converted into the oxide form.

Preferred compositions of the sacrificial metal layer and of the otherlayers of the multilayer system together with the preferred thicknessranges of the individual layers will emerge from the dependent claims.

The invention is described below in greater detail by means of anillustrative example that is compared with a comparative example of theprior art. To evaluate the properties of the layers, the measurementsand tests given below are carried out on the coated pane.

A. Measurement of the transmission T at 550 nm of a coated pane.

B. Measurement of the reflection color parameters in a laboratory system(DIN 5033)—an ISO zero standard is used as color reference. It isnecessary to maintain fixed tolerance values Δ on the color parametersof this reference standard, which values are defined in the followingmanner in the case of the multilayer system in question here, in theprestressed state:ΔL=±3.0; Δa=±1.4; Δb=−3.5 to +1.0.

C. Measurement of the electrical surface resistance using Veeco Instr.FPP 5000 instruments and an SQO HM-1 manual measurement instrument.

D. Measurement of the emissivity E using a Sten Löfving MK2 instrument.

E. Water seepage test according to DIN 50017 with visual evaluation.

F. Electrochemical resistance measurement (EMK test); this test isdescribed in Z. Silikattechnik 32 (1981), page 216. The test provides aconclusion regarding the quality of passivation of the covering layerlocated above the silver layer, and the corrosion behavior of the Aglayer.

G. Erichsen scrubbing test according to ASTM 2486, with visualevaluation.

H. Measurement of the scratch hardness: a needle under a certain weightis drawn over the coating at a defined rate. The weight in g for whichscratch lines are visible serves as a measurement of the scratchhardness.

I. Measurement of the scattered light, in %, with a light scatteringmeasurement instrument from the company Gardner.

COMPARATIVE EXAMPLE

In a continuous industrial coating plant, the multilayer system of theprior art (DE 39 41 027) was applied to float glass by the method ofreactive sputtering in a magnetic field, the thickness of the individuallayers being given each time in nm:glass/3TiO₂/22SnO₂/13Al:ZnO/12Ag/5TiAl/20SnO₂/10TiO₂.

The Al:ZnO layer was reactively sputtered using a ZnAl metal targetcontaining 2% Al by weight. The sacrificial metal layer was sputteredusing a metal target containing 64% Ti and 36% Al. The covering layerwas deposited by reactive sputtering using a metal titanium target.

The above tests carried out on several specimens before the heattreatment gave on average the following values: A. Transmission T₅₅₀ =76-77% B. Color parameters ΔL −0.1 Δa 4.47 Δb −5.31 C. Surfaceresistance R = 6.8-6.9 Ω D. Emissivity E = 7.8 E. Water seepage test Redspots F. EMK test 140 mV G. Scrubbing test Coating starts to debondafter 350 passes H. Scratch hardness 60-210 g I. Scattered light 0.17%

Several variously coated specimens, 60×80 cm in size, were heated to680-700° C. and prestressed by sudden cooling. The tests andmeasurements described below were then carried out on the prestressedglass specimens. The water seepage test, the EMK test, the scrubbingtest and the scratch hardness test were not carried out because, byexperience, it is known that these values do not deteriorate after theheat treatment operation. The tests carried out gave the followingresult: A. Transmission T₅₅₀ = 88.5% B. Color parameters ΔL 1.3 Δa 1.56Δb −3.95 C. Surface resistance R = 4.0-4.6 Ω D. Emissivity E = 5.8-6.8%I. Scattered light 0.35%

The increase in the light scattering factor, from 0.17% to 0.35%, as aresult of the heat treatment is still acceptable. However, an emissivityof 5.8-6.8% is too high for manufacturing insulating panes with a kvalue of 1.1 W/m²K. The color parameters after prestressing lie outsidethe tolerance limits. The glazing has, in reflection, a blue-reddishvisual appearance. Large variations in the thickness of the variouslayers also do not allow a neutral reflection color to be obtained withthe intended color values.

ILLUSTRATIVE EXAMPLE

The multilayer system according to the invention given below wasmanufactured on the same coating plant as that of the comparativeexample using, both for the deposition of the sacrificial metal layerand the deposition of the covering layer, a metal target consisting ofan alloy of 64% Ti by weight and 36% Al by weight:glass/25SnO₂/9Al:ZnO/11.5Ag/2TiAl(TiH_(x))/5Al:ZnO/33SnO₂/3Ti_(x)Al_(y)O_(z)N_(r).

The sacrificial metal layer was deposited in an Ar/H₂ (90/10 vol%)working gas mixture and the oxynitride covering layer was deposited inan Ar/N₂/O₂ working gas mixture.

The measurements and the tests on the coated glazing before the heattreatment gave the following values: A. Transmission T₅₅₀ = 78.3% B.Color parameters ΔL −0.9 Δa 2.80 Δb −3.8 C. Surface resistance R = 5.7 ΩD. Emissivity E = 6.6-6.7% E. Water seepage test No defect F. EMK test64 mV G. Scrubbing test No marks after 1 000 passes H. Scratch hardness150-260 g I. Scattered light 0.18%

After the prestressing operation, the same measurements and the sametests as in the case of the prestressed panes of the comparative examplewere carried out on several specimens. The tests gave the followingresults: A. Transmission T₅₅₀ = 88.3% B. Color parameters ΔL 1.0 Δa 1.2Δb −2.4 C. Surface resistance R = 3.6-4.0 Ω D. Emissivity E = 4.8-5.0 I.Scattered light 0.27%

Both on the thermally untreated coating and on the thermally treatedcoating, the values obtained demonstrate significant improvements. Inparticular, the thermally treated coating satisfies the predeterminedcolor parameters. The reflection color is substantially more neutralthan in the comparative example. The functional dependence betweensurface resistance and emissivity corresponds better to the physicaldependence and allows insulating glazing to be manufactured with a kvalue of 1.1 W/m²K. The proportion of scattered light is increasedsignificantly less by the heat treatment than in the comparativeexample. This indicates that the Ag layer is only slightly destructured.The result of the other tests, for example the water seepage test, theEMK test, the scrubbing test and the scratch hardness test that werecarried out on the thermally untreated specimens are better than theaverage. The multilayer system can be manufactured in a stable andreproducible manner on an industrial coating plant.

1. A low-emissivity multilayer system, capable of being highly stressedthermally, comprising a functional layer which comprises a silver, asacrificial metal layer placed above the silver layer, antireflectiondielectric layers and an oxide, nitride or oxynitride covering layer,wherein said sacrificial metal layer consists of Ti or an alloy of Tiand Zn and/or Al, and comprises chemically bonded hydrogen, and whereina ZnO layer optionally doped with Al and/or In is joined to saidsacrificial metal layer and in that the wherein said covering layerconsists of a titanium compound.
 2. The multilayer system as claimed inclaim 1, wherein said sacrificial metal layer consists of a TiAl alloycomprising 20 to 50% Al by weight.
 3. The multilayer system as claimedin claim 1, wherein said sacrificial metal layer has a layer thicknessof 1 to 5 nm.
 4. The multilayer system as claimed in claim 1, whereinsaid ZnO layer comprises 0.5 to 10% Al and/or In by weight.
 5. Themultilayer system as claimed in claim 4, wherein said ZnO layer has athickness of at least 3 nm.
 6. The multilayer system as claimed in claim1, wherein an SnO₂, Si₃N₄, ZnO, Al₂O₃ and/or SiO₂ layer is placed aspartial layer of the upper antireflection dielectric layer between theZnO layer and the covering layer.
 7. The multilayer system as claimed inclaim 1, wherein said covering layer consists of Al:ZnO/TiO₂, Al:ZnO/Ti,Zn_(x)Sn_(y)O_(z)/TiO₂, Zn_(x)Sn_(y)O_(z)/Ti, Zn_(x)Ti_(y)Al_(z)O_(r),Ti_(x)Al_(y)O_(z), Ti_(x)Al_(y), Ti_(x)Al_(y)N₂, Ti_(x)Al_(y)O_(z)N_(r),Zn_(x)Sn_(y)Sb_(z)O_(r)/TiO₂, Zn_(x)Sn_(y)Sb_(z)O_(r)/Ti orZn_(x)Sn_(y)Al_(z)O_(r)/TiO₂.
 8. The multilayer system as claimed inclaim 1, wherein the multilayer structure is:glass/SnO₂/Al:ZnO/Ag/TiAl(TiH_(x))/Al:ZnO/SnO₂/Al:ZnO/Ti_(x)Al_(y)O_(z)N_(r).